Method of inhibiting puffing in the manufacture of graphite bodies

ABSTRACT

THE IRREVERISBLE EXPANSION OF GRAPHITIC MATERIALS AT TEMPERATURES OF UP TO 2900%C., WHICH IS DUE TO THE EVOLUTION OF SULFUR FROM THE CARBON AGGREGATED USED AS STARTING MATERIAL, IS ELIMINATED BY INCORPORATION OF AS LITTLE AS 0.05 PART BY WEIGHT OF A TITANIUM OR ZIRCONIUM COMPOUND PER 100 PARTS OF CARBON AGGREGATE, E.G. TIO2, IN CONJUNCTION WITH THE CONVENTION &#34;PUFFING&#34; INHIBITORS OF THE ART.

United States Patent O 3,563,705 METHOD OF INHIBITING PUFFING IN THE MANUFACTURE OF GRAPHITE BODIES Lloyd 1. Grindstalf, Elizabethton, Mack P. Whittaker, Johnson City, and Michael F. Baud, Elizabethton, Tenn., assignors to Great Lakes Carbon Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 17, 1969, Ser. No. 807,963 Int. Cl. C01b 31/04 US. Cl. 23209.1 4 Claims ABSTRACT OF THE DISCLOSURE The irreversible expansion of graphitic materials at temperatures of up to 290= C., which is due to the evolution of sulfur from the carbon aggregate used as starting material, is eliminated by incorporation of as little as 0.05 part by weight of a titanium or zirconium compound per 100 parts of carbon aggregate, e.g. TiO in conjunction with the conventional puffing inhibitors of the art.

THE PRIOR ART In the manufacture of graphite electrodes and other graphite bodies, a petroleum coke of low sulfur content is the generally preferred raw material. The coke is first calcined at temperatures of 1000 or more, a process during which it loses its volatile components and some of its sulfur content. The calcined coke is then ground and mixed with a carbonizable binder such as pitch and the mixture is formed into the desired shape, for example by extrusion. The body thus obtained is carefully baked to calcining temperatures to carbonize the binder and set the mass, and the baked material is further heated to temperatures of over 2000 to cause graphitization.

One of the most serious difliculties encountered in this process is the undesirable sudden, irreversible expansion (commonly referred to as pulling) and even cracking of the shaped masses caused by the escape of sulfur during the heat treatments of the graphitizable mixtures. And obviously, as the supply of low sulfur coke diminishes due to exhaustion of the satisfactory petroleum sources, the necessity of employing cokes produced from high sulfur crude oils compounds the problem.

Among the methods that already have been devised to circumvent this expansion or pulling phenomenon, the most practical and widely adopted has been to add up to 10% by weight of an iron or calcium compound, preferably 0.5 to 5% of an oxide, to the graphitizable mixtures. The effect of these additives is to retard the pulling that would normally occur between about 1400 and 2500 C. with most petroleum cokes, so that it does not occur before a temperature of 2500 C. is reached. This, however, has been found to be only a partial solution to the problem 'since this retarding of the pulling merely delays the pulling of the graphitizable mass until temperatures of about 2600 to 2800 C. are reached.

THE OBJECTS OF THE INVENTION The present invention therefore contemplates the elimination of the delayed pufiing that takes place in graphitizable masses containing anti-pulling substances such as iron and calcium compounds. Another of its objects is to provide a process which will significantly minimize pulling without resort to the impractical expedient of heating the graphitizable mass at substantially lower than normal rates in cases where such an expedient is applicable. Another object is to increase the supply of coke usable for the manufacture of electrodes and related articles by rendering available high sulfur cokes which are 3,563,705 Patented Feb. 16, 1971 presently ineligible due to a propensity to expand severely during heat treatment to graphitization temperatures even in the presence of conventional anti-pulling agents.

A SUMMARY OF THE INVENTION These and other objects which shall become apparent in the course of the description of the invention, have been accomplished by incorporating a titanium or a zirconium compound into the graphitizable mixture of sulfur-containing coke, binder and conventional pulling inhibitor. It has thus been found that the joint action of the titanium-class compound and the iron or calcium oxide type of pulling inhibitor, which may consist of any of a variety of compounds of sulfide-forming metals including the alkali earth metals, essentially eliminates the expansion of graphitizable mixtures caused by the heat induced escape of sulfur under graphitizing conditions. For a typical sulfur coke-pitch mix containing from about 0.5 to 5% by weight or more of iron oxide as pulling inhibitor, a titanium or zirconium compound content of about 0.05 to 5 parts per parts of coke, calculated as TiO or ZrO has been found most effective. Larger proportions of titanium-class compounds will also be effective but are likely to create problems in certain applications because of the undesirable presence of larger quantities of residual titanium in the finished graphite article. The preferred proportion of titanium-class inhibitor in the graphitizable mixtures of the invention lies within the range of about 0.1 to 1 part per 100 parts of coke.

The preferred delayed pulling inhibitors include the oxides of titanium and zirconium as well as mixtures thereof and mixtures of said oxides with other anti-pulling metallic oxides. The mixtures may be natural or synthetic.

THE DETAILED DESCRIPTION OF THE INVENTION The following embodiments will further describe the invention. It must be understood that these examples are provided to illustrate the practice of the invention and are not intended as limitations beyond those imposed by the appended claims.

The carbon bodies in the examples were made from calcined petroleum cokes having a particle size distribution of 35 mesh to l00 mesh and a sulfur content of about 1% by weight. All the cokes used were needle cokes of the type described in US. Pats. 2,775,549 and 2,922,755 and exhibited irreversible expansion during graphitization. In each example, the selected coke was mixed in a standard manner with a coal tar pitch binder in proportions of 4:1 by weight. Particulate puffing inhibitors were added to the mix and blended uniformly as indicated and the mixtures were formed by hot pressing in an electrically heated mold, for example at 12,500 p.s.i.g. for 30 seconds at 100 C. The cylindrical bodies thus formed were baked to a temperature of about 850 C.

The extent of irreversible expansion exhibited by each ba-ked formulation as a function of heat treatment was measured with a graphite dilatometer. The dilatometer holding the baked carbon body was heated in a graphite tube furnace to temperature as high as 2900" C. at a rate of 14 C. per minute. A nitrogen atmosphere was maintained throughout the heating period. This dynamic puffing measurement technique is that used and described by Whittaker et al. in The Irreversible Expansion of Carbon Bodies During Graphitization published in Proceedings of the Division of Fuel Chemistry in the 156th Annual Meeting of the American Chemical Society, volume 12, No. 4, pp. 81-93 (September 1968). The technique is well established.

The results of these measurements and the inhibitors employed are reported in the following table. Significant puffing or expansion, when observed, is reported in terms of the temperature range over which it occurred.

fur-containing coke wherein a pulling inhibitor selected EFFECT OF PUFFING INHIBITORS ON GRAPHI'TIZABLE MIXTURES Coke Conventional Delayed pulling Ranges of temperatures over source iuhibitor inhibitor which pulling was observed Example:

co None None 1,7002,800 C.

. 2,6002,900 C., (delayed pulling.) No pulling to 2,900 C.

.do 0.5 p.p.h. F203 1.5 p.p.h. TiOzHfl No pulling. 6 ...d0 1.8 p.p.h. F0203". 0.2 p.p.h. TlOz D0.

7... 1.9 p.p.h. F0 0 0 1 p.p.h.TiO1.. Do.

8... h ,800 C. 0..- N0 pulling. Do.

11 Derby .do .do Do.

1 Parts/100 parts coke. 2 Added as ilmenite, i.e. 2 p.p.h. FeO- T10.

An examination of these results shows that the calcined needle cokes employed here, which all contain about 1% sulfur, exhibit steady irreversible expansion between the temperatures of 1700 to 2800 C. (Example 1). This puffing may be postponed or delayed by adding one of the conventional inhibitors to the graphitizable mixture, e.g. an oxide of iron. In such a case, no pulling will take place until about 2600 C. is reached and at that point striking and extensive expansion will occur (Example 2). It should be kept in mind that the extent of pulling and the temperatures at which it occurs will vary somewhat depending on the nature of the coke and on the exact sulfur content.

It is also evident that the delayed puffing inhibitors of this invention do not prevent the irreversible expansion of the graphitizable mixture when used alone (Examples 4 and 8). On the other hand, it is apparent from the results in the table that titanium and zirconium, in this instance as oxides, not only will suppress all pulling when used together with a conventional anti-pulling agent (Examples 57 and 91l), but also will do so at surprising low concentrations (Examples 6 and 7).

The delayed puffing inhibitors of this invention, i.e. compounds of titanium and zirconium, are equally effective in carbon bodies made with coke particles larger than 35 to l00 mesh which normally exhibit extensive pulling when iron oxide is used alone.

from the group consisting of iron compounds, calcium compounds, and mixtures thereof is incorporated into a mixture of the coke and a binder to inhibit pulling during heat treatment, the improvement which comprises additionally incorporating into the coke-binder mixture a delayed pulling inhibitor selected from the group consisting of titanium compounds, zirconium compounds, and mixtures thereof.

2. The method of claim 1 wherein the pulling inhibitor consists of at least 0.5 part per hundred parts by weight of coke and the delayed pufiing inhibitor consists of 0.05 to 5 parts per hundred parts by weight of coke.

3. The method of claim 2 wherein the pulling inhibitor consists of about 0.5 to 5 parts per hundred parts by weight of coke of an oxide of iron.

4. The method of claim 2 wherein the delayed pulling inhibitor consists of about 0.1 to 1 part per parts by weight of coke of titanium dioxide.

References Cited UNITED STATES PATENTS 2,814,076 11/1957 Gartland 26429 3,338,993 8/1967 Juel et al 26429 3,506,745 4/1970 Juel et al. 23209.1X

EDWARD J. MEROS, Primary Examiner US. Cl. X.R. 26429 

